Exhaust member

ABSTRACT

An exhaust member having two or more exhaust ports separated by a partition wall extending between an inner wall of a tubular portion, wherein said partition wall has the minimum thickness A in a range within ½ of the length of said partition wall from its longitudinal middle point as a center, when viewed in an arbitrary transverse cross section of said tubular portion (including an opening end surface) having said partition wall; wherein said partition wall becomes gradually wider outside said range; and wherein each cuter surface of said partition wall exists in a region sandwiched by (a) an inner line comprising a parallel line H 1,  H 2  separate from the longitudinal centerline of said partition wall by a distance of A/2, and an arc R 1,  R 2  tangentially connected to said parallel line H 1,  H 2  and said inner wall and having a radius r 1,  r 2,  wherein both r 1  and r 2  are ⅓×A or more, meeting r 1 +r 2 =1.9A, and (b) outer line comprising a parallel line H 3,  H 4  separate from the longitudinal centerline of said partition wall by a distance of 3/2×A, and an arc R 3,  R 4  tangentially connected to said parallel line H 3,  H 4  and said inner wall and having a radius r 3,  r 4,  wherein both r 3  and r 4  are ⅓×A or more, meeting r 3 +r 4 =4A.

FIELD OF THE INVENTION

The present Invention relates to an exhaust member for engines, such asan exhaust manifold, a turbine housing, etc., which is free from thelikelihood of cracking to its outer surface.

BACKGROUND OF THE INVENTION

Some exhaust members for multi-cylinder (series-four-cylinder,series-six-cylinder, etc.) engines, such as exhaust manifolds, turbinehousings, etc., have divided exhaust ports to prevent the interferenceof an exhaust gas discharged from each engine cylinder, and backpressureincrease. The division of the exhaust port stabilizes the performanceand operation of the engine.

As one example of exhaust members, FIG. 8 shows an exhaust manifold Mconnected to cylinders #1 to #4 of a series-four-eylinder engine E, anda turbine housing T connected to a flange of the exhaust manifold M.FIG. 9 is an enlarged cross-sectional view taken along the line Z-Z inFIG. 8. Combustion usually occurs in the order of cylinders #1-#3-#4-2in the series-four-eylinder engine E.

The exhaust manifold M comprises branch tubes BR1-BR4 connected to fourexhaust outlets EX1-EX4 of the engine E, and a downstream-side tubularportion 30 m to which the branch tubes BR1-BR4 converge. The tubularportion 30 m comprises a flange 31 m formed at a downstream-side endperiphery, and two exhaust ports Pa, Pb separated by a partition wall 32m. The branch tubes BR1, BR4 converge to the exhaust port Pb, and thebranch tubes BR2, BR3 converge to the exhaust port Pa.

An upstream-side tubular portion 30 t of the turbine housing T comprisesa flange 31 t formed at an upstream-side end periphery, and two intakeports Qa, Qb separated by a partition wall 32 t. The flange 31 t hassubstantially the same shape as that of the flange 31 m of the exhaustmanifold M. The partition wall 32 t and the intake ports Qa, Qb areshaped and arranged such that when the flange 31 t is connected to theflange 31 m of the exhaust manifold M via a gasket S with bolts BT, thepartition wall 32 m of the exhaust manifold M is smoothly connected tothe partition wall 32 t of the turbine housing T, and the exhaust portsPa, Pb are smoothly connected to the intake ports Qa, Qb.

Because the downstream-side tubular portion 30 m of the exhaust manifoldM and the upstream-side tubular portion 30 t of the turbine housing Thave essentially the same shape and function as is clear from FIG. 8,explanation will be made only on the downstream-side tubular portion 30m. Its explanation is applicable to the upstream-side tubular portion 30t of the turbine housing T, or tubular portions of other similar exhaustmembers, as it is.

As shown in FIG. 9, a partition wall 32 connected to the inner wall ofthe tubular portion 30 is repeatedly subjected to compression stress andtensile stress by heating and cooling due to the start and stop of theengine E. However, because the expansion and shrinkage of the partitionwall 32 is constrained by the flange 31 formed at a periphery of thetubular portion 30, cracks CRK are likely to be generated in aconnecting portion 34 of the partition wall 32 and the tubular portion30. When the cracks CRK reach the outer surface of the tubular portion30, an exhaust gas is likely to leak.

The mechanism of generating cracks CRK will be explained in detailreferring to FIGS. 10( a)-10(e). FIG. 10( a) shows the basic shapes ofthe partition wall 32 m and the exhaust port Pa, Pb of the exhaustmanifold M in the opening end surface 33. As shown in FIG. 10( b), whenan engine (not shown) is operated, the partition wall 32 is heated by ahigh-temperature exhaust gas. As shown in FIG. 10( c), however, thepartition wall 2 cannot expand freely because of a strong constraint bythe flange 31, resulting in plastic deformation and the generation ofcompression strain. When the engine stops go that the exhaust manifold Mis cooled to room temperature, the partition wall 32 tends to thermallyshrink, exceeding thermal plastic deformation as shown in FIG. 10( d).However, because it is strongly constrained by the flange 31 as shown inFIG. 10( e), large tensile strain is generated in the partition wall 32and/or the connecting portion 34. When heating and cooling are repeatedby the start and stop of the engine, it is likely that cracks CRKgenerated in the partition wall 32 turn the exhaust ports Pa and Pbcommunicable, and that cracks CRK generated in the connecting portion 34reach the outer surface of the tubular portion 30.

When the exhaust ports Pa and Pb become communicable by cracks CRKgenerated in the partition wall 32, exhaust interference andbackpressure increase occur. Also, the cracks CRK reaching to the outersurface of the tubular portion 30 allow an exhaust gas to eject from theexhaust ports Pa, Pb, and turn the operation of a turbine housing, ifany, unstable, resulting in engine performance decrease.

To prevent cracks from generating in the partition wall and the tubularportion of the exhaust manifold, JP 60-95118 U proposes, as shown inFIG. 11, a partition wall 32 having a slit SLT deeper than the thicknessof a flange 31 to absorb thermal expansion and shrinkage. It has beenfound, however, that the slit SLT causes turbulence in an exhaust gasflowing through the ports, resulting in backpressure increase and thusengine power decrease.

JP 2-39529 U proposes, as shown in FIG. 12, an exhaust manifold locallyhaving a thin-wall portion TW in a partition wall 32, so that thethin-wall portion TW is easily deformed to alleviate thermal stress whenthe partition wall 32 is thermally deformed. The thin-wall portion TWlocally formed in the partition wall 32 can prevent the generation ofcracks CRK, without disturbing the exhaust gas unlike when the slit SLTis formed in the partition wall 32 (JP 60-95118 U). It has been found,however that cracks CRK reaching the outer surface of the exhaust memberare likely formed depending on the shape of the connecting portion 34 ofthe partition wall 32 and the tubular portion 30. Also, in the shape ofthe partition wall 32 shown in FIG. 12, thick connecting portions 34make the overall exhaust manifold extremely heavy.

JP 7-217438 A proposes, as shown in FIG. 13, an exhaust manifoldcomprising exhaust ports Pa, Pt each having a substantially trapezoidalcross section, and arcuate connecting portions 34 each having a smallradius of curvature Rs for connecting a partition wall 32 and a linearinner wall 35, thereby dispersing thermal stress in the linear innerwall 35. It has been found, however, that cracks CRK reaching the outersurface of the exhaust member are likely formed depending on the shapeof the connecting portion 34 connecting the partition wall 32 and thelinear inner wall 35. Also, the exhaust port is restricted to have asubstantially trapezoidal cross section, resulting in extremely smallfreedom of design.

OBJECTS OF THE INVENTION

Accordingly, an object of the present invention is to provide an exhaustmember free from the likelihood of cracking to its outer surface,without extreme restriction of the cross section shape of an exhaustport,

DISCLOSURE OF THE INVENTION

As a result of intense research in view of the above object it has beenfound that it is difficult to completely prevent cracking due to thermalstrain by expansion and compression, in a connecting portion between apartition wall and a tubular portion without extremely increasing theweight of an exhaust member, and that the above problem can be overcomeby inducing cracks, if any, to a center portion of the partition wallwhile preventing them from propagating to the outer surface of theexhaust member. The present invention has been completed based on suchfindings.

Thus, the exhaust member of the present invention has two or moreexhaust ports separated by a partition wall extending between an innerwall of a tubular portion, said partition wall having the minimumthickness A in a range within ½ of the length of said partition wallfrom its longitudinal middle point as a center, and becoming graduallywider outside that range, when viewed in an arbitrary transverse crosssection of said tubular portion (including an opening end surface)having said partition wall; and each outer surface of said partitionwall existing in a region sandwiched by (a) each inner line comprising aparallel line H1, H2 separate from a longitudinal centerline of saidpartition wall by a distance of A/2, and an arc R1, R2 tangentialyconnected to said parallel line H1, H2 and said inner wall and having aradius r1, r2, wherein both r1 and r2 are ⅓×A or more, meetingr1+r2=1.9A, and (b) each outer line comprising a parallel line H3, H4separate from the longitudinal centerline of said partition wall by adistance of 3/2×A, and an arc R3, R4 tangentially connected to saidparallel line H3, H4 and said inner wall and having a radius r3, r4,wherein both r3 and r4 are ⅓×A or more, meeting r3+r4=4A.

The radii r1, r2 of said arcs R1, R2 preferably meet the condition ofr1+r2=2.5A.

It is preferable that the minimum thickness A of said partition wall is2-10 mm, and that said partition wall is tangentially connected to saidinner wall with an arc having a radius of 2-13 mm in a transverse crosssection of said tubular portion having said partition wall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a front view showing a downstream-side opening end surfaceof an exhaust member according t a preferred embodiment of the presentinvention.

FIG. 1( b) is an enlarged view showing a portion X in FIG. 1( a).

FIG. 2( a) is a front view showing a downstream-side opening end surfaceof an exhaust member according to another preferred embodiment of thepresent invention.

FIG. 2( b) is a front view showing a downstream-side opening end surfaceof an exhaust member according to a further preferred embodiment of thepresent invention.

FIG. 2( c) is a front view showing a downstream-side opening end surfaceof an exhaust member according to a still further preferred embodimentof the present invention.

FIG. 3( a) is a front view showing a downstream-side opening end surfaceof an exhaust member according to a still further preferred embodimentof the present invention.

FIG. 3( b) is a front view showing a downstream-side opening end surfaceof an exhaust member according to a still further preferred embodimentof the present invention.

FIG. 3( c) is a front view showing a downstream-side opening end surfaceof an exhaust member according to a still further preferred embodimentof the present invention.

FIG. 3( d) is a front view showing a downstream-side opening end surfaceof an exhaust member according to a still further preferred embodimentof the present inventions

FIG. 4( a) is a perspective view showing the shape of a test piece usedin Example 1.

FIG. 4( b) is a front view showing the shape of a test piece used inExample 1.

FIG. 4( c) is an enlarged front view showing the shape of a partitionwall of a test piece used in Example 1.

FIG. 4( d) is a front view showing the shape of a test piece used inComparative Example 1.

FIG. 4 (e) is a front view showing the shape of a test piece used inComparative Example 2.

FIG. 5( a) is a front view showing the shape of a test piece used inExample 2.

FIG. 5( b) is an enlarged front view showing the shape of a partitionwall of a test piece used in Example 2.

FIG. 5( c) is a front view showing the shape of a test piece used inComparative Example 3.

FIG. 6 is a schematic view showing a thermal fatigue test machine.

FIG. 7( a) is a perspective view showing the turbine housing of Example3 after the thermal fatigue test.

FIG. 7( b) is a perspective view showing the turbine housing ofComparative Example 4 after the thermal fatigue test.

FIG. 8 is a cross-sectional view showing one example of the exhaustmember connected to a series-four-cylinder engine.

FIG. 9 is an enlarged cross-sectional view taken along the line Z-Z inFIG. 8.

FIG. 10 is a schematic view explaining the mechanism of generatingcracks.

FIG. 11 is a front view showing a downstream-side opening end surface ofthe exhaust member described in JU 60-95118 A.

FIG. 12 is a front view showing a downstream-side opening end surface ofthe exhaust member described in JU 2-39529 A,

FIG. 13 is a front view showing a downstream-side opening end surface ofthe exhaust member described in JP 7-217438 A.

DESCRIPTION OF THE BEST MODE OF THE INVENTION

The exhaust member of the present invention will be explained in detailbelow referring to the attached drawings, though the present inventionis not restricted to those shown in the figures. It should be noted thatthe same reference numerals are assigned to the same parts or portions,with their explanation omitted.

First Embodiment

FIG. 1( a) is a front view showing an opening end surface 3 of anexhaust member in the first embodiment, and FIG. 1( b) is an enlargedview showing a portion X in FIG. 1( a). This exhaust member has a flange1 having a substantially rectangular contour, and a partition wall 2having a center portion with a substantially linear outer surface andboth end portions each with a curved outer surface. The partition wall 2has the minimum thickness A in a range within ½ of the length of thepartition wall 2 with its longitudinal middle point O as a center, andits curved outer surfaces are gradually wider outside that range (on theend portion sides).

Portions divided by a tangent line L1 common to exhaust ports Pa and Pbshown in FIG. 1( a) are called “flange 1” and “partition wall 2”connected to the flange 1 via a connecting portion 4. On the paper ofthe figure, the flange 1 is above the tangent line L1, while thepartition wall 2 is below the tangent line L1. With a tangent line L2common to the exhaust ports Pa and Pb similarly drawn on the end of thepartition wall 2 opposite to the L1-side end, the smallest distancebetween the tangent line L1 and the tangent line L2 is defined as thelength of the partition wall 2. In a range within ¾ of the length of thepartition wall 2 from a longitudinal middle point O of the partitionwall 2 as a center, a line connecting middle points of the width of thepartition wall 2 is defined as a longitudinal centerline C of thepartition wall. Outside the above range, a tangent line of thelongitudinal centerline C at a position of ⅜ of the length of thepartition wall 2 is defined as longitudinal centerline C.

Each outer surface 2 a of the partition wall 2 should exist on oroutside each inner line (shown by the chain line) comprising a parallelline H1, E2 separate from the longitudinal centerline C of the partitionwall 2 by a distance of A/2, and an arc R1, R2 having a radius r1, r2which is tangentially connected to the parallel line H1, H2 and theinner wall 5 of the tubular portion 10. The term “tangentiallyconnected” used herein means that the tangent line of each arc K1, R2 isin alignment with that of each parallel line H1, H2 at a contact pointof the arc R1, R2 and the parallel line H1, H2. The same is true of thecontact point of the arc R1, E2 and the inner wall 5. Accordingly, eacharc R1, R2 corresponds to an arc having a radius r1, r2 inscribed to theparallel line H1, H2 and the inner wall 5.

The radii r1 and r2 should meet the condition of r1+r2=1.9A, When eachouter surface 2 a of the partition wall 2 is closer than that to thecenterline C, the partition wall 2 is too thin to avoid cracking. Whenany one of r1 and r2 is extremely small, the connecting portion 4 of thepartition wall 2 and the inner wall 5 has too large a curvature to avoidstress concentration, resulting in high likelihood of cracking.Therefore, both of r1 and r2 should be ⅓×A or more, preferably ½×A ormore. Although r1=r2 in this embodiment, r1 may not be equal to r2 as ina subsequent embodiment. Particularly in such a case, r1 and r2 shouldnot be too small.

Because a high-temperature, high-pressure exhaust gas flows alternatelythrough exhaust ports Pa, Pb separated by the partition wall 2, thepartition wall 2 should have such thickness as to hold sufficienthigh-temperature strength. Because stress is concentrated particularlyin the connecting portion 4, the connecting portion 4 should be thickerthan the center portion. However, too thick a partition wall 2 makes theexhaust member too heavy. Accordingly, each outer surface 2 a of thepartition wall 2 should exist on or inside each outer line (shown by thechain line) comprising a parallel line H3, H4 separate from thelongitudinal centerline C by a distance of 3/2×A, and an arc R3, R4having a radius r3, r4 and tangentially connected to the parallel lineH3, H4 and the inner wall 5 of the tubular portion 10. Like the are R1,R2, the arc R3, R4 corresponds to an arc having a radius r3, r4 andinscribed to the parallel line H3, H4 and the inner wall 5.

The radii r3 and r4 should meet the condition of r3+r4=4A. When eachouter surface 2 a of the partition wall 2 is more distant than that fromthe centerline C, the partition wall 2 is so thick that an exhaustmember is heavy. When any one of r3 and r4 is extremely small, theconnecting portion 4 of the partition wall 2 and the inner wall 5 hastoo large a curvature to avoid stress concentration, resulting in highlikelihood of cracking. Therefore, both of r3 and r4 should be ⅓×A ormore, preferably ½×A or more. Although r3=r4 in this embodiment, r3 maynot be equal to r4 as in a subsequent embodiment. Particularly in thatcase, attention should be paid to avoid that r3 and r4 are too small.

In the center region 21 and the tapered region 4 a, the outer surface 2a of the partition wall 2 may have a straight contour, but it preferablyhas a slightly curved contour. The slightly curved contour may not bearcuate. At a position at which the distance of the partition wall 2from the middle point O is ⅜ of the length of the partition wall 2, thethickness A2 of the partition wall 2 is preferably 1.3 times or more,more preferably 1.5 times or more, of the minimum thickness A of thepartition wall 2. The center region 21 is smoothly connected to thetapered region 4 a.

The connecting portion 4 b is preferably a curved line smoothlyconnecting the outer surface 2 a of the partition wall 2 to the innerwall 5, more preferably an arc tangentially connected to the outersurface 2 a and the inner wall 5. The arc may have such a radius thatthe outer surface 2 a of the partition wall 2 exists between said innerline and said outer line, and the radius of the arc is preferably ⅓×A ormore, more preferably ½×A or more.

Because each outer surface 2 a of the partition wall 2 exists in aregion B1, B2 sandwiched by said inner line and said outer line,cracking occurs predominantly in said center region 21 when a largethermal stress is applied to the partition wall 2, with other regionssuffering little cracking. Even if there are cracks near the connectingportion 4 of the partition wall 2 and the flange 1, they propagate nottoward the flange 1 but toward the partition wall 2 away from the flange1, so that cracks penetrating from the exhaust ports Pa or Pb to theouter surface of the exhaust member are hardly generated. Accordingly,the above shape of the partition wall 2 can provide an exhaust memberfree fi-om cracks in the tubular portion 10 without increasing theweight of the exhaust member.

In the exhaust member of the present invention, it is more preferablethat the radii r1, r2 of the arcs R1, R2 meet the condition of r1+r2=2.5A, that the minimum thickness A of the partition wall is 2-10 mm,and that each outer surface of the partition wall is tangentiallyconnected to the inner wall of the exhaust port with an arc having aradius of 2-13 mm in an arbitrary transverse cross section of the pipe.With this structure, there is less likelihood of generating cracksextending from the exhaust port to the outer surface of the exhaustmember.

Second Embodiment

FIG. 2( a) shows an opening end surface 3 of an exhaust member in thesecond embodiment. This exhaust member is substantially the same as thatof the first embodiment except that both partition wall 2 and exhaustports are inclined, so that it should meet all the conditions of thefirst embodiment.

Third Embodiment

FIG. 2( b) shows an opening end surface 3 of an exhaust member in thethird embodiment. This exhaust member is substantially the same as thatof the first embodiment except that a partition wall 2 has an S shape,so that it should meet all the conditions of the first embodiment.

Fourth Embodiment

FIG. 2( c) shows an opening end surface 3 of an exhaust member in thefourth embodiment. This exhaust member is substantially the same as thatof the second embodiment except that a partition wall 2 has an S shape,so that it should meet all the conditions of the first embodiment.

Fifth Embodiment

FIG. 3( a) shows an opening end surface 3 of an exhaust member in thefifth embodiment. This exhaust member is substantially the same as thatof the first embodiment except that the opening end surface 3 has acircular shape, so that it should meet all the conditions of the firstembodiment.

Sixth Embodiment

FIG. 3( b) shows an opening end surface 3 of an exhaust member in thesixth embodiment. This exhaust member is substantially the same as thatof the fifth embodiment except that both partition wall 2 and exhaustport are inclined, so that it should meet all the conditions of thefirst embodiment.

Seventh Embodiment

FIG. 3( c) shows an opening end surface 3 of an exhaust member in theseventh embodiment. This exhaust member is substantially the same asthat of the fifth embodiment except that a partition wall 2 has an Sshape, so that it should meet all the conditions of the firstembodiment.

Eighth Embodiment

FIG. 3( d) shows an opening end surface 3 of an exhaust member in theeighth embodiment. This exhaust member is substantially the same as thatof the sixth embodiment except that a partition wall 2 has an S shape,so that it should meet all the conditions of the first embodiment.

In the above second to eighth embodiments, too, the partition wall 2 hasthe minimum thickness A in a range (center region 4 a) within ½ of thelength of the partition wall from the longitudinal middle point O of thepartition wall as a center, and its outside region (end region 40) has agradually increasing width. Also, each outer surface of the partitionwall exists in a region sandwiched by (a) each inner line comprising aparallel line H1, H2 separate from the longitudinal centerline C of thepartition wall by a distance of A/2, and an arc R1, R2 having a radiusr1, r2 and tangentially connected to the parallel line H1, H2 and theinner wall, wherein both r1 and r2 are ⅓×A or more, meeting r1+r2=1.9A,and (b) each outer line comprising a parallel line H3, H4 separate fromthe longitudinal centerline C of the partition wall by a distance of3/2×A, and an arc R3, R4 having a radius of r3, r4 and tangentiallyconnected to the parallel line H3, H4 and the inner wall, wherein bothr3 and r4 are ⅓×A or tore, meeting r3+r4=4A. This reduces the generationof cracks extending from the exhaust ports to the outer surface of theexhaust member without extremely increasing the weight of the exhaustmember, thereby providing an exhaust member without extremelyrestricting the cross section shape of the exhaust port.

The present invention will be described in further detail referring toExamples below without intention of restricting the present inventionthereto.

EXAMPLE 1

A test piece TP having the shape shown in FIG. 4( a) was produced fromheat-resistant austenitic cast steel. The test piece TP had a thicknessof 20 mm, the tubular portion 10 had a thickness FW of 20 mm, and thepartition wall 2 had a length of 80 mm. FIG. 4( b) shows an opening endsurface 3 of the test piece TP, and FIG. 4( c) is ail enlarged viewshowing the partition wall 2. The partition wall 2 has a 6-mm-thickflat-plate-shaped center region 21 in a range within ½(40 mm) of thelength of the partition wall 2 from the longitudinal middle point O as acenter, and an end region 40 comprising a tapered region 4 a and aconnecting portion 4 outside the flat-plate-shaped center region 21. Theminimum thickness A of the partition wall 2 is 6 mm, the same as that ofthe center region 21, and the tapered region 4 a has a gradually andlinearly increasing width from the end of the center region 21. Thethickness A2 is 10 mm at a position separate from the longitudinalmiddle point O of the partition wall 2 by a distance of 30 mm, ⅜ of thelength of the partition wall 2. The connecting portion 4 is in an arcshape having a radius of 7 mm and tangentially connected to the taperedregion 4 a and the inner wall 5 of the tubular portion 10. Table 1 showsthe size of the test piece TP.

With the partition wall 2 formed as described above, each outer surface2 a of the partition wall 2 existed in a region (hatched portion B1, B2)sandwiched by (a) each inner line comprising a parallel line H1, H2separate from the longitudinal centerline C of the partition wall 2 by adistance of A/2, namely 3 mm, and an arc R1, R2 tangentially connectedto the parallel line H1, H2 and the inner wall 5 and having a radius ofr1=r2=5.7 mm, wherein both r1 and r2 are ⅓×A or more, meetingr1+r2=1.9A, and (b) each outer line comprising a parallel line H3, H4separate from the longitudinal centerline C of the partition wall 2 by adistance of 3/2×A, namely 9 mm, and an arc R3, R4 tangentially connectedto the parallel line H3, H4 and the inner wall and having a radius ofr3=r4=12 mm, wherein both r3 and r4 are ⅓×A or more, meeting r3+r4=4A.

The test piece TP was subjected to a thermal fatigue test by a thermalfatigue-test apparatus described in Japanese Patent 2533885. In thethermal fatigue test machine 50 shown in FIG. 6, LPG from ail LPG source52 and air from a compressor 53 are supplied to a burner 51, and air isforcedly supplied to a combustion chamber 54, so that LPG is ignited inthe combustion chamber 54 and burned in the burner 51. Flame 55 from theburner 51 is injected into the combustion chamber 54, and the resultanthigh-temperature combustion gas is caused to flow to the test piece TPvia a combustion gas passage 56 a of a cooling block 56 to heat the testpiece TP. The combustion gas passage 56 a is cooled by water circulatingin the cooling block 56 having cooling water inlet and outlet. The testpiece TP is provided with a sheath-type thermocouple 57 at its inlet.The thermal fatigue test was conducted by repeating cycles eachcomprising two steps of (i) heating the test piece TP until thetemperature detected in the sheath-type thermocouple 57 reached 950° C.amid then keeping it at that temperature for 10 minutes, and (ii)stopping the supply of the combustion gas and keeping it for 10 minutes,until cracking was observed in the test piece TP. The thermal fatiguetest revealed that the test piece TP of Example 1 had cracks in alongitudinal center portion of the partition wall 2, but was free fromcracks extending from the exhaust port to the outer surface of the testpiece TP.

COMPARATIVE EXAMPLE 1

As shown in FIG. 4( d), a test piece TP was produced in the same manneras in Example 1, except that the tapered region 4 a of the partitionwall 2 was made to have a constant thickness of 6 mm, meaning that therewas substantially no tapered region 4 a, and that the connecting portion4 was formed by an arc having a radius of 2 mm and tangentiallyconnected to the outer surface 2 a of the partition wall 2 and the innerwall 5 of the tubular portion 10. The minimum thickness A of thepartition wall 2 was 6 mm, the same as the thickness of the centerregion 21, and the thickness A2 of the partition wall 2 was 6 mm at aposition of 30 mm, ⅜ of the length of the partition wall 2 from themiddle point O. Table 1 shows the size of the test piece TP. Thepartition wall 2 of this test piece TP had each outer surface 2 a inportions other than the region (hatched portion B1, B2) described inExample 1, which was sandwiched by the inner and outer lines. Further,whenever any one of the radii r1-r4 was ⅓×A or more, meeting r1+r2=1.9A,and r3+r4=4A, the partition wall 2 had each outer surface 2 a existingbeyond the region (hatched portion B1, B2) sandwiched by the inner andouter lines. The test piece TP of Comparative Example 1 was subjected toa thermal fatigue test as in Example 1, resulting in cracks extendingfrom the connecting portion of the partition wall and the flange to theexhaust port to the outer surface of the test piece TP.

COMPARATIVE EXAMPLE 2

As shown in FIG. 4( e), a test piece TP was produced in the same manneras in Example 1, except that the thickness A2 of the partition wall 2was 30 mm at a position of ⅜ of the length of the partition wall fromthe longitudinal middle point O of the partition wall. Table 1 shows thesize of the test piece TP. The partition wall 2 of this test piece TPhad each outer surface 2 a existing beyond the region (hatched portionB1, B2) described in Example 1 which was sandwiched by the inner andouter lines. The test piece TP was subjected to the same thermal fatiguetest as in Example 1, revealing that cracks were generated in thelongitudinal center portion of the partition wall 2, without cracksextending from the exhaust port to the outer surface of the test pieceTP. However the test piece TP of Comparative Example 2 was as heavy as1.1 times the test piece TP of Example 1, resulting in 10-% decrease inthe cross section area of the exhaust port.

EXAMPLE 2

As shown in FIG. 5( a), a test piece TP was produced in the same manneras in Example 1, except that the partition wall was in an S shape, FIG.5( b) is an enlarged view showing the partition wall of the test pieceTP. With the longitudinal middle point O of the partition wall 2 as acenter, the partition wall 2 has a 6-mm-thick, flat-plate-shaped centerregion 21 in a range within 112 of the length of the partition wall 2,and an end region 40 comprising a tapered region 4 a and a connectingportion 4 outside the flat-plate-shaped center region 21. The centerregion 21 is inclined by an angle θ₁ of 30° relative to the partitionwall 2 of Example 1 and the tapered region 4 a is inclined by angle η₂of −45° relative to the partition wall 2 of Example 1, so that theoverall partition wall 2 is in an S shape. The minimum thickness A ofthe partition wall 2 is 6 mm, the same as the thickness of the centerregion 21, and the tapered region 4 a is gradually linearly wideningfrom the end of the center region 21, so that the thickness A2 is 10 mmat a position of ⅜ of the length of the partition wall 2 from thelongitudinal middle point O of the partition wall 2. The center region21 is tangentially connected to the tapered region 4 a with arcs Ri andRo having radii ri (3 mm) and ro (9 mm) in a bent portion 23. Amongthose formed by the center region 21 and the tapered region 4 a, an arcconnecting the outer surfaces 2 a of the partition wall 2 on a smallerangle side is expressed by Ri, and an arc on the other side is expressedby Ro. The connecting portion 4 is formed by an arc Ra having a radiusof 10 mm and an arc Rb having a radius of 5 mm both tangentiallyconnected to the tapered region 4 a and the inner wall 5 of the tubularportion 10. An arc with an obtuse angle between the partition wall 2 andthe inner wall 5 was Ra, and an arc with an acute angle was Rb. Table 1shows the size of the test piece TP.

With the partition wall thus formed, each outer surface 2 a of thepartition wall 2 existed in a region (hatched portion B1, B2) sandwichedby (a) each inner line comprising a parallel line H1, H2 separate fromthe longitudinal centerline C of the partition wall by a distance ofA/2, namely 3 mm, and an arc R1, R2 tangentially connected to theparallel line H1, H2 and the inner wall and having a radius r1, r2,wherein r1 of 10 mm was on the obtuse angle side, and r2 of 5 mm was onthe acute angle side, meeting r1+r2=2.5A, and (b) each outer linecomprising a parallel line H3, H4 separate from the longitudinalcenterline C of the partition wall by a distance of 3/2×A, namely 9 mm,and an arc R3, R4 tangentially connected to the parallel line H3, H4 andthe inner wall and having a radius r3, r4, wherein r3 of 16 mm was onthe obtuse angle side, and r4 of 8 mm on the acute angle side, meetingr3+r4=4A. The same thermal fatigue test as in Example 1 revealed thatcracking occurred near the longitudinal center of the partition wall,but there were no cracks extending from the exhaust port to the outersurface of the test piece TP.

COMPARATIVE EXAMPLE 3

As shown in FIG. 5( c), a test piece TP was produced in the same manneras in Example 2, except that the tapered region 4 a of die partitionwall 2 had a constant thickness of 6 mm, the same as that of the centerregion 21, and that it had arcs Ra and Rb having radii of 8 mm and 2 mm,respectively, with substantially no tapered region 4 a. Table 1 showsthe size of the test piece TP.

With the partition wall thus formed, the outer surface 2 a of thepartition wall 2 existed beyond the region (hatched portion B1, B2)sandwiched by (a) each inner line comprising the parallel line H1, H2and the arc R1, R2 tangentially connected to the parallel line H1, H2and the inner wall, and (b) each outer line comprising the parallel lineH3, H4 and the arc R3, R4 tangentially connected to the parallel lineH3, H4 and the inner wall, even when any radii r1-r4 were ⅓×A or more,meeting r1+r2=1.9A, and r3+r4=4A. The same thermal fatigue test as inExample 1 revealed that there were cracks extending from the exhaustport to the outer surface of the test piece TP in the connectingportions of the partition wall and the flange.

TABLE 1 Comparative Comparative Comparative No. Example 1 Example 1Example 2 Example 2 Example 3 Length of 80 mm 80 mm 80 mm 80 mm 80 mmPartition Wall Thickness of 6 mm 6 mm 6 mm 6 mm 6 mm Center RegionMinimum 6 mm 6 mm 6 mm 6 mm 6 mm Thickness A A2⁽¹⁾ 10 mm 6 mm 30 mm 10mm 6 mm Radius of Arc r = 7 mm r = 2 mm r = 7 mm ra = 10 mm ra = 8 mmRegion rb = 5 mm rb = 2 mm Inclination⁽²⁾ of θ₁ = 0° θ₁ = 0° θ₁ = 0° θ₁= 30° θ₁ = 30° Partition Wall θ₂ = 0° θ₂ = 0° θ₂ = 0°  θ₂ = −45°  θ₂ =−45° Position⁽³⁾ of — — — 20 mm 20 mm Bent Portion Radius of Bent — — —ri = 3 mm ri = 3 mm Portion ro = 9 mm ro = 9 mm Note: ⁽¹⁾A2 wasthickness at a position of 30 mm from the middle point of the partitionwall. ⁽²⁾Inclination to the partition wall of Example 1, wherein θ₁ isan angle of the center region, and θ₂ is an angle of the tapered region.⁽³⁾Distance from the middle point of the partition wall.

EXAMPLE 3

A turbine housing Ta shown in FIG. 7( a) was produced. The turbinehousing Ta is used in series-four-cylinder, high-performance gasolineengine (not shown) with a displacement of 2000 cc. A turbine in theturbine housing was rotated by the pressure of an exhaust gas dischargedfrom the engine and gathered by an exhaust manifold, to drive acompressor concentric with the turbine to compress the mixed gas, whichis returned to the engine to increase the power of the engine.

As shown in FIG. 7( a), an opening end surface 3 of the turbine housingTa has a substantially similar shape to that of the test piece TP ofExample 1 shown in FIG. 4( b). Accordingly, the shape of its partitionwall 2 will be explained referring to FIG. 4( b). The partition wall 2has a length of 40 mm and the minimum thickness A of 3 mm. With thelongitudinal middle point O as a center, the partition wall 2 has a3-mm-thick, flat-plate-shaped center region 21 in a range within ½ ofthe length of the partition wall 2, and there is an end region 40comprising a tapered region 4 a and a connecting portion 4 outside theflat-plate-shaped center region 21. The minimum thickness A of thepartition wall 2 is 3 mm, the same as the thickness of the center region21, the tapered region 4 a becomes gradually linearly wider from an endof the center region 21, and the thickness A2 is 5 mm at a position of15 mm, ⅜ of the length of the partition wall 2, from the longitudinalmiddle point O of the partition wall 2. The connecting portion 4 was inan arc shape having a radius of 3.5 mm, which tangentially connected thetapered region 4 a to the inner wall 5 of the tubular portion 10.

With the partition wall thus formed, each outer surface 2 a of thepartition wall 2 existed in a region (hatched portion B1, B2) sandwichedby (a) each inner line comprising a parallel line H1, H2 separate fromthe longitudinal centerline C of the partition wall by a distance ofA/2, namely 1.5 mm, and an arc R1, R2 tangentially connected to theparallel line H1, H2 and the inner wall and having a radius r1, r2,wherein both r1, r2 were 2.85 mm, meeting r1+r2=1.9A, and (b) each outerline comprising a parallel line H3, H4 separate from the longitudinalcenterline C of the partition wall by a distance of 3/2×A, namely 4.5mm, and an arc r3, r4 tangentially connected to the parallel line H3, H4and the inner wall and having a radius r3, r4, wherein both r3, r4 were6 mm, meeting r3+r4=4A. Portions of the turbine housing Ta other thanthe flange and the partition wall, which were mainly as thick as 2.5-5.5mm, were formed from heat-resistant austenitic cast steel, through apredetermined heat treatment and machining.

The same thermal fatigue test as in Example 1 was conducted on theturbine housing Ta using the thermal fatigue test machine 40. Thethermal fatigue test comprised 1000 cycles each comprising two steps of(i) heating the turbine housing Ta until the temperature of a centerportion of the partition wall 2 reached 1000° C., and keeping it for 10minutes, and (ii) stopping the supply of a combustion gas to cool it,and keeping it for 10 minutes, FIG. 7( a) shows cracks CRK generated inthe turbine housing Ta after the thermal fatigue test. The cracks CRKwere generated substantially in the center portion of the partition wall2, but no cracks penetrating to the outer surface of the turbine housingwere observed.

COMPARATIVE EXAMPLE 4

The turbine housing Tb shown in FIG. 7( b) was produced like the turbinehousing Ta of Example 3, except that the tapered region 4 a of thepartition wall 2 had a constant thickness of 3 mm, the same as that ofthe center region 21, meaning that there was substantially no taperedregion 4 a, and that an arc tangentially connected to the partition wall2 and the inner wall 5 had a radius of 2 mm. The opening end surface 3of the turbine housing Tb has a substantially similar shape to that ofthe test piece TP of Comparative Example 1 shown in FIG. 4( d).

In the turbine housing Tb, the outer surface 2 a of the partition wall 2existed beyond the region (hatched portion B1, B2) sandwiched by (a)each inner line comprising a parallel line H1, H2 separate from thelongitudinal centerline C of the partition wall by a distance of A/2,and an arc R1, R2 tangentially connected to the parallel line H1, H2 andthe inner wall, and (b) each outer line comprising a parallel line H3,H4 separate from the longitudinal centerline C of the partition wall bya distance of 3/2×A, and an arc R3, R4 tangentially connected to theparallel line H3, H4 and the inner wall, even when any radii 41-r4 were⅓×A or more, meeting r1+r2=1.9A and r3+r4=4A.

A thermal fatigue test conducted on the turbine housing Tb under thesame conditions as in Example 3 revealed that cracks CRK penetrating tothe outer surface of the turbine housing Tb were generated in 318cycles. FIG. 7( b) shows the cracks CRK. In the turbine housing Tb, anexhaust gas in the exhaust port Pa or Pb ejected outside through thecracks CRK, causing exhaust interference and making the operation of theturbine housing unstable, resulting in decrease in engine performance.

The above Examples verify that the exhaust member of the presentinvention is free from cracks extending from the exhaust poll to theouter surface of the exhaust member, without suffering from extremeweight increase.

EFFECT OF THE INVENTION

Because the exhaust member of the present invention having the abovestructure is free from cracks penetrating to the outer surface withoutweight increase and substantial restriction in the cross section shapeof the exhaust port, the engine operation is stabilized withoutperformance decrease.

1. An exhaust member having two or more exhaust ports separated by apartition wall extending between an inner wall of a tubular portion,wherein said partition wall has the minimum thickness A in a rangewithin ½ of the length of said partition wall from its longitudinalmiddle point as a center, when viewed in an arbitrary transverse crosssection of said tubular portion (including an opening end surface)having said partition wall, and wherein each outer surface of saidpartition wall exists in a region sandwiched by (a) an inner linecomprising a parallel line H1, H2 separate from a longitudinalcenterline of said partition wall by a distance of A/2, and an arc R1,R2 tangentially connected to said parallel line H1, H2 and said innerwall and having a radius r1, r2, wherein both r1 and r2 are ⅓×A or more,meeting r1+r2=1.9A, and (b) an outer line comprising a parallel line H3,H4 separate from the longitudinal centerline of said partition wall by adistance of 3/2×A, and an arc R3, R4 tangentially connected to saidparallel line H3, H4 and said inner wall and having a radius r3, r4,wherein both r3 and r4 are ⅓×A or more, meeting r3+r4=4A.
 2. The exhaustmember according to claim 1, wherein radii r1, r2 of said arcs R1, R2meet the condition of r1+r2=2.5A.
 3. The exhaust member according toclaim 1, wherein the minimum thickness A of said partition wall is 2-10mm, and wherein each outer surface of said partition wall istangentially connected to said inner wall with an arc having a radius of2-13 mm in an arbitrary transverse cross section of said tubularportion.
 4. The exhaust member according to claim 2, wherein the minimumthickness A of said partition wall is 2-10 mm, and wherein each outersurface of said partition wall is tangentially connected to said innerwall with an arc having a radius of 2-13 mm in an arbitrary transversecross section of said tubular portion.